Mixing and casting

The applied mixing sequence was:

1. The aggregate already in the mixer was mixed for 30 seconds

2. Powder was added from the powder pre-silo and mixing continued to a total of 60 second.

3. Water and silica fume slurry was added over a period of 30 seconds while mixing

4. Air entraining agent was added and with a 30 second delay the superplasticizer was added

5. Mixing was continued for 120 seconds after addition of superplasticizer to a total of 240 seconds.

The fresh concrete properties were then tested and if in accordance with target ranges the concrete was discharged to a 500 liter crane bucket, and used to cast test cylinders and cubes or a small concrete block of 1 x 1 x 0,2 m.

For the production of a large concrete block (1 x 2 x 0,2 m) two batches of concrete were required. For SCC both batches had to meet fresh concrete requirements, while for slump concrete the two batches had to be homogenized and the combined batch had to meet the fresh concrete requirements. Homogenization was performed in a 500 liter pan mixer discharging the concrete back into the crane bucket.

Casting of slump concrete was performed in layers of 30 - 40 cm. Each layer was  poker vibrated according to the Danish HETEK guidelines. SCC was cast at a target rate of 20 m/hr corresponding to a casting time of 6 minutes pr. element.